CVE-2026-33216

NATS has MQTT plaintext password disclosure

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, for MQTT deployments using usercodes/passwords: MQTT passwords are incorrectly classified as a non-authenticating identity statement (JWT) and exposed via monitoring endpoints. Versions 2.11.14 and 2.12.6 contain a fix. As a workaround, ensure monitoring end-points are adequately secured. Best practice remains to not expose the monitoring endpoint to the Internet or other untrusted network users.

CVSS 3.1 · 8.6 High EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-29785

NATS Server panic via malicious compression on leafnode port

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.14 and 2.12.5, if the nats-server has the "leafnode" configuration enabled (not default), then anyone who can connect can crash the nats-server by triggering a panic. This happens pre-authentication and requires that compression be enabled (which it is, by default, when leafnodes are used). Versions 2.11.14 and 2.12.5 contain a fix. As a workaround, disable compression on the leafnode port.

CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-27889

NATS: Pre-auth remote server crash via WebSocket frame length overflow in wsRead

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server. This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.

CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33217

NATS allows MQTT clients to bypass ACL checks

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, when using ACLs on message subjects, these ACLs were not applied in the `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

CVSS 3.1 · 7.1 High EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33218

NATS has pre-auth server panic via leafnode handling

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable leafnode support if not needed or restrict network connections to the leafnode port, if plausible without compromising the service offered.

CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33219

NATS is vulnerable to pre-auth DoS through WebSockets client service

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-server before authentication; this requires sending a corresponding amount of data. This is a milder variant of CVE-2026-27571. That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable websockets if not required for project deployment.

CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33247

NATS credentials are exposed in monitoring port via command-line argv

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, if a nats-server is run with static credentials for all clients provided via argv (the command-line), then those credentials are visible to any user who can see the monitoring port, if that too is enabled. The `/debug/vars` end-point contains an unredacted copy of argv. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, configure credentials inside a configuration file instead of via argv, and do not enable the monitoring port if using secrets in argv. Best practice remains to not expose the monitoring port to the Internet, or to untrusted network sources.

CVSS 3.1 · 7.4 High EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33222

NATS JetStream has an authorization bypass through its Management API

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, users with JetStream admin API access to restore one stream could restore to other stream names, impacting data which should have been protected against them. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, if developers have configured users to have limited JetStream restore permissions, temporarily remove those permissions.

CVSS 3.1 · 4.9 Medium EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33248

NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, when using mTLS for client identity, with `verify_and_map` to derive a NATS identity from the client certificate's Subject DN, certain patterns of RDN would not be correctly enforced, allowing for authentication bypass. This does require a valid certificate from a CA already trusted for client certificates, and `DN` naming patterns which the NATS maintainers consider highly unlikely. So this is an unlikely attack. Nonetheless, administrators who have been very sophisticated in their `DN` construction patterns might conceivably be impacted. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, developers should review their CA issuing practices.

CVSS 3.1 · 4.2 Medium EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33223

NATS Server: Incomplete Stripping of Nats-Request-Info Header Allows Identity Spoofing

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, the NATS message header `Nats-Request-Info:` is supposed to be a guarantee of identity by the NATS server, but the stripping of this header from inbound messages was not fully effective. An attacker with valid credentials for any regular client interface could thus spoof their identity to services which rely upon this header. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

CVSS 3.1 · 6.4 Medium EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server

CVE-2026-33249

NATS: Message tracing can be redirected to arbitrary subject

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.11.0 and prior to versions 2.11.15 and 2.12.6, a valid client which uses message tracing headers can indicate that the trace messages can be sent to an arbitrary valid subject, including those to which the client does not have publish permission. The payload is a valid trace message and not chosen by the attacker. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

CVSS 3.1 · 4.3 Medium EPSS < 1% KEV · Not listed

Vendors

Linuxfoundation Nats

Products

Nats-server Nats Server